202 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 2.0000 1.8000 1.6000 1.4000 z 1. 2000 0 1.0000 0.8000 0.6000 0.4000 0.2000 •Dermis •- Total Skin i i i i i i i i i i i i i i 1200 1400 1600 1800 2000 2200 2400 WAVELENGTH (nm) Figure 2. NIR absorption spectra of total skin, dermis, and epidermis. versus r = -0.720 for n = 106). The band at 1100 nm is the wavelength at which the absorbance of skin is minimal. We therefore used the difference in absorbance at 1100 and 1936 nm in the rest of the study, which is, as in the in vitro experiment, better than other ones. The regression line in Figure 5, constructed using the overall data obtained at TO (before beginning treatment), is a mathematical representation of the decrease in the spectra illustrated in Figure 4. Despite the large number of values (n = 310), the correlation coefficient (r = -0.536, p 0.001) remained very high. For the overall data at TO, the changes in the overall clinical score (Figure 6) as a function of the individual "scaling" and "roughness" scores correlated strongly with the presence of scales (r = 0.76), but weakly with roughness (r - 0.43). The roughness score no longer changed above an overall score of 3, a phenomenon reflected by the correlations between absorbance and these two individual scores: the "scaling" score was still strongly correlated (r = -0.409) with IR absorbance (Figure 7a), while the "roughness" score was only weakly correlated (Figure 7b) (r = -0.344). It is worth noting that the three other descriptive scores ("papyrac•," squames, irritation) are not correlated either to the difference in absorbance (r = - 0.15, - 0.19, - 0.13) or to the overall score (r = 0.25, 0.20, 0.28). The correlation between electrical conductance and the clinical score was significant but linear only for scores below 2.5 (Figure 8). Beyond the conductance is independent of the score. The correlations between descriptive scores values and conductance concern the "papyrac•" scores (r = -0.331, p 0.01)and roughness (r - -0.370, p 0.01). Figure 9 compares the overall results obtained with the five cosmetic preparations, comparing the treated and untreated legs, for the three following parameters: change in

NEAR-INFRARED SPECTROSCOPY 203 0,26 0.24 0.16 0.14 r = 0.98 n =52 p 0.0001 I i I I I I 0 5 10 15 20 25 3o WATER CONTENT (ø7o) Figure 3. In vitro experiment: Influence of the water content of stratum corneum samples on the NIR absorption measured at 1936 nm and 1100 nm. near-infrared absorbance, change in conductance, and change in clinical dryness score. The change in the near-infrared parameter (Figure 9a) showed that all the treatments except preparation D had statistically significant activity. Products A, C, and E were significantly more effective than product B, which, in turn, was more effective than product D. In terms of conductance, product D was again statistically ineffective, but products A, C, and E were significantly more effective than products B and D, which had comparable effects (Figure 9b). Finally, the reduction in the dryness score (Figure 9c) was significant for products A, B, C, and E, which showed similar activity, but not for product D. On the basis of near-infrared absorbance, which correlated with the clinical score, product B was distinguished from products A, C, D, and E. DISCUSSION With the equipment described, the near-infrared radiation penetrated deeply into the skin, although the superficial layers had a clear influence, as shown in Figures 2 and 4. The study of isolated stratum corneum samples with varying degrees of relative humid- ity showed that the difference in absorbance at 1936 and 1100 nm indeed reflected water content, since, for values between 0 and 30% (at which water is bound), there was a linear relationship between absorbance and water content. It was also this difference in absorbance that was best correlated with the overall skin dryness score, which, as mentioned above, was the sum of several clinical parameters (roughness, scaling, "cig- arette paper" aspect, etc.). The correlation was far better than that between conductance values and the degree of